An ongoing difficulty with correctly attributing and quantifying ad impressions is that, unlike direct-interaction scenarios, there is both a physical and temporal disconnect between the impression created by the ad and any action taken by the user as a result thereof. When a user sees a clickable ad that takes him or her to a landing page, or is presented with an advertisement containing an embedded phone number on a call-capable mobile device, the user may interact with that advertisement directly and immediately and that interaction may be identified and logged to track ad effectiveness.
By contrast, when a user is exposed to an advertisement via an information display that does not permit or allow for direct ad interaction (such as an information display monitor or an electronic billboard) or is presented with an ad containing a phone number on a device that cannot make phone calls (i.e. a desktop or laptop or netbook computer or a media tablet/media player not configured to make telephone calls), it is more difficult to determine if a user acted based on the advertisement.
Specifically in the context of telephone numbers, a user may write down a number and call it at a later time, or may call the number immediately but from a different device. This creates some difficulties for distributors of advertising content with respect to determining the appropriate price/cost of advertising space on a publisher's media outlet since there is no measurable, causal connection between a user viewing the advertisement and making a subsequent telephone call and/or taking some other kind of action.